BUG: tri: prevent Triangulation from modifying specified input

triplot(x, y, simplex) should not modify the simplex array as a side
effect.

lib/matplotlib/tests/test_triangulation.py

@@ -122,3 +122,12 @@ def test_tripcolor():
     plt.subplot(122)
     plt.tripcolor(triang, facecolors=Cfaces, edgecolors='k')
     plt.title('facecolors')
+
+def test_no_modify():
+    triangles = np.array([[3, 2, 0], [3, 1, 0]], dtype=np.int32)
+    points = np.array([(0, 0), (0, 1.1), (1, 0), (1, 1)])
+
+    old_triangles = triangles.copy()
+    tri = mtri.Triangulation(points[:,0], points[:,1], triangles)
+    edges = tri.edges
+    assert_array_equal(old_triangles, triangles)

lib/matplotlib/tri/triangulation.py

@@ -80,8 +80,9 @@ def __init__(self, x, y, triangles=None, mask=None):
                 neighbors = np.asarray(dt.triangle_neighbors, dtype=np.int32)
                 self._neighbors = np.roll(neighbors, 1, axis=1)
         else:
-            # Triangulation specified.
-            self.triangles = np.asarray(triangles, dtype=np.int32)
+            # Triangulation specified. Copy, since we may correct triangle
+            # orientation.
+            self.triangles = np.array(triangles, dtype=np.int32)
             if self.triangles.ndim != 2 or self.triangles.shape[1] != 3:
                 raise ValueError('triangles must be a (?,3) array')
             if self.triangles.max() >= len(self.x):